In general, when metal sheets are used as the exterior walls of diverse buildings, the metal sheets molded to form variously curved surfaces have been used for finishing materials of the building exterior walls in order to improve the sense of beauty of the whole city in line with unique designs of the buildings. Most conventional metal sheets with curved surfaces have been molded by a ‘method for molding a curved surface on a metal sheet’ disclosed in Korean Laid-open Patent No. 10-2009-0055348.
However, according to the method for molding a curved surface which is disclosed in Korean Laid-open Patent No. 10-2009-0055348, a metal sheet with a desired curved surface in a specific shape is obtained simply by pressing a metal sheet positioned between upper and lower molds having a number of form punches which are hydraulically operated. Therefore, it is impossible to produce a sheet molded to form a more precise and gorgeous multi-dimensional curved surface. Moreover, it is impossible to absolutely eliminate the spring back phenomenon of the molded metal sheet.